Statics, equilibrium sphere in a groove on an incline plane

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Discussion Overview

The discussion revolves around a statics problem involving a smooth homogeneous sphere resting in a groove on an inclined plane. Participants are attempting to determine the angle θ, measured from the horizontal, for which the reaction forces on each side of the groove equal the force supported by an end plate. The conversation includes various approaches to solving the problem, including the application of equilibrium equations and the interpretation of forces acting on the sphere.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant states that the equations and diagrams presented are incorrect and emphasizes the 3D nature of the problem.
  • Another participant suggests that an angle of 45 degrees could work based on their interpretation of the forces involved.
  • Several participants express confusion over the interpretation of the forces acting on the sphere and the relationship between the forces on the sides of the groove and the end plate.
  • There is a discussion about the need to eliminate variables and the correct handling of simultaneous equations to solve for θ.
  • Some participants propose using unit vector notation for clarity, while others argue that the ratios of forces are more critical than their actual values.
  • Participants debate the correct application of trigonometric functions in their equations and the implications of using specific numerical values versus symbolic representation.
  • One participant suggests simplifying the problem by setting a force equal to 1 to eliminate it from the equations.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the correct approach to solving the problem. There are multiple competing views on the interpretation of the forces, the appropriate angles, and the methods for eliminating variables in the equations.

Contextual Notes

There are unresolved issues regarding the assumptions made about the forces and their directions, as well as the mathematical steps necessary to arrive at a solution. The discussion reflects a range of interpretations and approaches without a definitive resolution.

  • #31
J-dizzal said:
Where does F cancel out?
Well right at the beginning you could cancel it out by dividing both sides by F. (Zero divided by F is zero.)

It should cancel at a later step too, but you're making a mistake in one of your steps... You're dividing one side by F but not the other side.

There also seems to be another mistake: you are turning α into θ at the last step. [edit: also the 2 appears to be missing somewhere]

(I haven't read this thread, so I'm just trusting that the initial equation is correct.)
 
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  • #32
J-dizzal said:
F-(2Fsin(α))/cosθ)=0
That's already wrong. You lost a sin(theta) somewhere.
 
  • #33
Nathanael said:
Well right at the beginning you could cancel it out by dividing both sides by F. (Zero divided by F is zero.)

It should cancel at a later step too, but you're making a mistake in one of your steps... You're dividing one side by F but not the other side.

There also seems to be another mistake: you are turning α into θ at the last step. [edit: also the 2 appears to be missing somewhere]

(I haven't read this thread, so I'm just trusting that the initial equation is correct.)

I keep getting the same answer now, still wrong though;
F-(2Fsin(α))/cos(θ))sin(θ)=0
1-(2sinα/cosθ)sinθ=0
cosθ-2sinαsinθ=0
-2sinαsinθ=-cosθ
-2sinα=-cosθ/sinθ
tanθ=1/2sinα
θ=arctan(1/sinα)
θ=50.87 degrees.​
 
  • #34
J-dizzal said:
tanθ=1/2sinα
θ=arctan(1/sinα)
Check that step.
 
  • #35
haruspex said:
Check that step.
θ=arctan(1/2sinα)
=50.87 incorrect
 
  • #36
J-dizzal said:
θ=arctan(1/2sinα)
=50.87 incorrect
There's another error in the working in the image attached to the OP. Didn't spot it before. You've swapped the 24 degrees and the 66 degrees.
 
  • #37
haruspex said:
There's another error in the working in the image attached to the OP. Didn't spot it before. You've swapped the 24 degrees and the 66 degrees.
yea!
Thanks haruspex.
 

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